Don't leak memory if a cgroup is mounted multiple times

Don't leak memory if a cgroup is mounted multiple times

It is possible (expected/likely in Fedora 15) for a cgroup controller
to be mounted in multiple locations at the same time, due to bind
mounts. Currently we leak memory if this happens, because we overwrite
the previous 'mountPoint' string. Instead just accept the first match
we find.

* src/util/cgroup.c: Only accept first match for a cgroup
  controller mount